System for determining a lens position

ABSTRACT

A system for determining lens position includes a first sensor component disposed on a stationary housing of a camera. A second sensor component is disposed on a rotating lens component of the camera. A processor is operatively connected to the first and second sensory components to identify the position of the rotating lens component of the camera based on an angle between the first and second sensor components.

GOVERNMENT RIGHTS STATEMENT

This invention was made with government support under contract numberHR0011-13-C-0068 awarded by Defense Advanced Research Projects Agency.The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to optics, and more particularly todetermining the lens position within a camera

2. Description of Related Art

A variety of systems can be used to determine the position of a lens inan optical system. For example, in a typical consumer autofocus camera,an electrical motor can be used to move a lens and the control signalsto the motor can be used to infer the final position of the lens.However, autofocus systems such as these can consume a relatively highamount of power, and can have limited accuracy.

Knowing the position of a lens in an optical system can be important indetermining the distance to an object being imaged. One example of a usefor knowing the distance to the object is for parallax correcting imagestaken from different viewpoints.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purpose. However, there is still a needin the art for improved systems and methods for determining lensposition. The present disclosure provides a solution for this need.

SUMMARY OF THE INVENTION

A system for determining lens position includes a first sensor componentdisposed on a stationary housing of a camera. A second sensor componentis disposed on a rotating lens component of the camera. A processor isoperatively connected to the first and second sensory components toidentify the position of the rotating lens component of the camera basedon an angle between the first and second sensor components. In certainembodiments, the system can include a second camera operativelyconnected to the processor such that the first camera can be a longwavelength infrared camera and the second camera can be a shortwavelength infrared camera.

The system can further include a memory operatively connected to theprocessor. The memory can include program instructions to calculate adistance to a point of focus of the camera based on a position of therotating lens component using an angle of rotation between the first andsecond sensor components. The memory can include instructions recordedthereon that, when read by the processor, cause the processor toparallax correct an image from the second camera based on the distancebetween the point of focus to the focal plane of the camera and an anglebetween the first and second sensor components.

A camera includes a housing and a lens rotatable relative to thehousing. A first magneto-resistive sensor is disposed on the housing. Asecond magneto-resistive sensor is disposed on the rotating lenscomponent. A processor is operatively connected to the first and secondmagneto-resistive sensors to identify the position of the rotating lenscomponent of the camera based on an angle between the first and secondmagneto-resistive sensors.

These and other features of the systems and methods of the subjectdisclosure will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosureappertains will readily understand how to make and use the devices andmethods of the subject disclosure without undue experimentation,preferred embodiments thereof will be described in detail herein belowwith reference to certain figures, wherein:

FIG. 1 is a schematic of an exemplary embodiment of a system fordetermining lens position constructed in accordance with the presentdisclosure, showing first and second cameras;

FIG. 2 is a schematic view of the images received from the first andsecond cameras of FIG. 1, showing parallax;

FIG. 3 is a cutaway perspective view of a portion of the system of FIG.1, showing sensor components disposed on the first camera;

FIG. 4 is a cutaway perspective view of another exemplary embodiment ofa first camera showing sensor components having capacitor platesdisposed in the first camera to form a variable capacitor; and

FIG. 5 is a schematic axial end view of an exemplary embodiment of alens position sensor, showing a system with four capacitor plates.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of a system foridentifying lens position in accordance with the disclosure is shown inFIG. 1 and is designated generally by reference character 100. Otherembodiments of systems in accordance with the disclosure, or aspectsthereof, are provided in FIGS. 2-5, as will be described.

With reference to FIG. 1, a system 100 is shown that can determine thelens position of a first camera and electronically determine distance toa point of focus to correct parallax between multiple cameras. The pointof focus of a lens system is controlled by moving a lens element orcomponent relative to the image plane location using either a threadedbarrel housing the lens system, a cam surface and a follower, or thelike. The rotation of the lens system is directly translated into linearmotion of the lens component along the optical axis, with respect to theimage plane.

FIG. 1 illustrates overlapping fields of view 106, 108 of first andsecond cameras 102, 104 which are laterally spaced a constant distanceapart relative to each other. The first and second cameras 102, 104 arespaced apart along a common plane. As will be understood by thoseskilled in the art, first and second cameras 102, 104 can be positionedrelative to each other in any other suitable way. The first and secondcameras 102, 104 can focus on objects 110, 112 a distance d1, d2,respectively, for displaying on a screen, for example, a heads-updisplay. The first camera 102 can be a long wavelength infrared camera(LWIR). The second camera 104 can be a short wave infrared camera(SWIR). The first and second cameras 102, 104 include a housing 120(shown in FIG. 3) and a lens component 124 manually rotatable relativeto the housing 120. Images displayed from the second camera 104 arealtered to produce a parallax corrected composite image on a displayscreen including image information from both cameras 102, 104.

The term parallax as used herein includes the displacement due toseparation between the optical axes. In other words, parallax is basedon the separation between the two cameras. The parallax between firstand the second images is further dependent on the distance to theobject. Therefore, if the distance to the object is known, the parallaxbetween the two images can be determined and used to adjust one or bothof the images. For example, the pixels of one image may be translated tocompensate for parallax. For example, a composite image showing featuresof both the LWIR camera 102 and the SWIR camera 104 can be produced withparallax correction so LWIR and SWIR features are properly aligned inthe composite image. As will be understood, the parallax may differ fordifferent parts of the images, if the distance to the imaged object orarea varies within the image. The parallax may be determined for onlyone part of the image or independently for different parts of the image.If the parallax is determined for only one part of the image, this partcan be determined in different ways. For example, the central portion ofthe image can be selected by default. As another example, it may bepossible for an operator to select a portion of the image for which theparallax should be determined, for example, the portion containing anobject of interest.

FIG. 2 schematically illustrates images produced by the first and secondcameras 102, 104 of system 100 prior to correcting for parallax. Firstimage portions 202, 212 imaged by the first camera 102 and second imageportions 204, 214 imaged by the second camera 104, are taken of the samescene at the same time. Images 202 and 212 are essentially the same asimages 204 and 214, respectively, but are slightly shifted with respectto each other because of the distance between the first and secondcameras 102, 104. For simplicity, the objects shown are a circle 112 anda square 110. In FIG. 1, the circle 112 is farther away from the cameras102, 104 than the square 110. Therefore, the displacement d2′ of theimages of the squares 212, 214 is greater than the displacement d1′ ofthe images of the circles 202, 204. The pixels of images 204, 214 fromthe second camera 104 can be translated horizontally a distance d1′ andd2′ to create a composite image showing the features of the first andsecond cameras 102, 104 corrected for parallax.

In order to determine the distances d1′, d2′ required to translatepixels from the second camera 104, the respective distances d1 and d2 tothe objects 110, 112 from the first camera 102 must be determined. Inthe present disclosure, and as described in more detail below, thedistances d1 and d2 to the point of focus 110, 112 of the first camera102 are determined based on the rotatable lens component position whenthe first camera 102 is focused on objects 110, 112. FIG. 3 shows firstcamera 102 of system 100. System 100 for determining lens position isbased on the axial position of the lens relative to the housing 120 ofcamera 102. A first sensor component 302 is disposed on the housing 120of the first camera 102. A second sensor component 304 is disposed onthe rotating lens component 124 of the first camera 102. The first andsecond sensors 302,304 are each operatively connected to a processor 130(shown in FIG. 1). The sensor components 302, 304 can be magneticsensors, for example, lightweight magneto-resistive sensors. The lenscomponent is shown and described as a rotating lens component, however aslidable lens that translates forward and backward with respect to thecamera housing is also contemplated.

Rotation of the lens component 124 relative to the housing 120 causesthe rotatable lens component 124 to move in a direction transverse tothe housing 120 and closer to objects 110, 112. Once the rotatable lenscomponent 124 is circumferentially rotated a desired distance to focuson objects 110, 112, sensor component 302 generates a signal based onthe strength and direction of the magnetic field caused by the other,which is indicative of the relative position of sensor component 304.The position of the sensor component 304 can then be determined by theprocessor 130. The processor 130 calculates distances d1 and d2 from thefirst camera 102 based on the angle of rotation 320 between the firstand second sensor components 302, 304. More specifically, the angle ofrotation 320 between the two sensor components 302, 304 is used by theprocessor 130 to calculate the position of the rotatable lens component124, which is used to infer distances d1 and d2 to the objects 110 and112, respectively. The use of an angular measurement provides a methodof accurately determining lens position. In typical camera systems, thedistance over which a lens system moves is extremely small relative tothe very large shift in position of the point of focus. One degree ofrotation could correspond to a very small translation in lens position.For example, one full rotation may move the lens system 0.5 mm. Onedegree of rotation would then correspond to 0.0014 mm, or 1.4 microns,of motion in the lens system. While it is very difficult to measuremovement of only 1.4 microns, it is much simpler to measure one degreeof rotation accurately.

The operation of processor 130 may be controlled with computerexecutable instructions, i.e., a program carrying instructions which canbe executed by the processor. One or more memory units, here shown asmemory 132, are operatively connected to the processor 130. The memory132 is used to store computer executable instructions to be executed bythe processor 130 when performing the functions of system 100 describedherein.

With reference to FIG. 1, the second camera 104 is operatively connectedto the processor 130. Once the processor 130 calculates the distances d1and d2, the processor 130 parallax corrects one or both images, forexample, images 204, 214. In other words, the pixels of the images 204and 214 viewed from the second camera 104 are translated to align withthe corresponding images 202 and 212 of the first camera 102. In thismanner, a parallax corrected composite image including features from thefirst and second cameras 102, 104 is shown on the display screen. Thisallows images in two different spectra, e.g., LWIR and SWIR, to becomposited to show useful information from both.

With reference to FIGS. 4 and 5, a first camera 102 for calculating thedistance to the point of focus from the first camera 102 is shown with adifferent embodiment of sensor components. In this embodiment, an arrayof capacitor plates 402, 404, 406 are disposed on a lens barrel assembly410. In this embodiment, three capacitor plates 402, 404 and 406 areshown to comprise the array of capacitor plates, however it will beunderstood that any suitable number of plates can be used.

A rotating capacitor 408 plate is disposed on a lens barrel 410. Each ofthe capacitor plates 402, 404, 406, 408, is operatively connected to theprocessor 130. By placing the capacitor plates 402, 404, 406, 408 inthis configuration, the capacitor plates 402,404, 406, 408 create avariable capacitor system in which capacitance varies based on theposition of the lens barrel 410. The electrical capacitance, and thusmeasured electrical charge, of any of the three capacitor plates, isproportional to the amount of area overlap between the rotatingcapacitor and any given capacitor of the array. As shown, the array ofcapacitor plates 402, 404, 406 is positioned circumferentiallysurrounding the rotating capacitor plate 408. As such the area ofoverlap 420 can extend between one or more of the capacitor plates 402,404, 406. The capacitance is used by processor 130 to calculate theangle of rotation of the lens barrel 410 and thus the distance to thepoint of focus. FIG. 5 shows schematically three capacitor plates 402,404, 406. Each capacitor plate 402, 404, 406 extends approximately 120°degrees around the rotating plate 408.

The methods and systems of the present disclosure, as described aboveand shown in the drawings, provide for a system for identifying lensposition with superior properties including correcting for parallaxbetween two cameras based on the lens position. While the apparatus andmethods of the subject disclosure have been shown and described withreference to preferred embodiments, those skilled in the art willreadily appreciate that changes and/or modifications may be made theretowithout departing from the spirit and scope of the subject disclosure.

What is claimed is:
 1. A system for determining lens position: a firstsensor component disposed on a stationary housing of a camera; a secondsensor component disposed on a rotating lens component of the camera;and a processor operatively connected to the first and second sensorycomponents to identify the position of the rotating lens component ofthe camera based on an angle between the first and second sensorcomponents.
 2. The system of claim 1, further comprising a memoryoperatively connected to the processor including program instructions tocalculate a distance to a point of focus of the camera based on an angleof rotation between the first and second sensor components.
 3. Thesystem of claim 2, further including a second camera operativelyconnected to the processor wherein the memory includes programinstructions to transform an image from the second camera to align withan image from the camera.
 4. The system of claim 3, wherein the firstcamera is a long wavelength infrared camera.
 5. The system of claim 4,wherein the second camera is a short wavelength infrared camera
 6. Thesystem of claim 1, wherein the processor is operatively connected to amemory, wherein the memory includes instructions recorded thereon that,when read by the processor, cause the processor to: calculate a distancefrom a point of focus to a focal plane of a camera based on a positionof the rotating lens component using an angle of rotation between thefirst and second sensor components.
 7. A system as recited in claim 6,wherein the memory includes instructions recorded thereon that, whenread by the processor, cause the processor to: parallax correct an imagefrom a second camera based on the distance between the point of focus tothe focal plane of the camera and an angle between the first and secondsensor components.
 8. A camera, comprising: a housing; a lens componentrotatable relative to the housing; a first magneto-resistive sensordisposed on the housing; a second magneto-resistive sensor disposed onthe lens; and a processor operatively connected to the first and secondmagneto-resistive sensors to identify the position of the rotating lenscomponent of the camera based on an angle between the first and secondmagneto-resistive sensors.
 9. The camera of claim 8, further comprisinga memory operatively connected to the processor including programinstructions to calculate a point of focus of the camera based on anangle of rotation between the first and second magneto-resistivesensors.
 10. The camera of claim 9, further including a second cameraoperatively connected to the processor wherein the memory includesprogram instructions to transform an image from the second camera toalign with an image from the camera.
 11. The camera of claim 10, whereinthe camera is a long wavelength infrared camera.
 12. The camera of claim11, wherein the second camera is a short wavelength infrared camera. 13.The camera of claim 8, wherein the processor is operatively connected toa memory, wherein the memory includes instructions recorded thereonthat, when read by the processor, cause the processor to: calculate adistance from a point of focus to a focal plane of a camera based on aposition of the rotating lens component using an angle of rotationbetween the first and second magneto-resistive sensors.
 14. A camera asrecited in claim 13, wherein the memory includes instructions recordedthereon that, when read by the processor, cause the processor to:parallax correct an image from a second camera based on the distancebetween the point of focus to the focal plane of the camera and an anglebetween the first and magneto-resistive sensors.